SPECIAL SENSES

Senses : any of the physical processes by which stimuli are received, transduced, and conducted as impulses to be interpreted in the brain.

The special senses consist of the eyes, ears, nose, throat and skin.
Each of these organs have specialized functions that make if possible for us to experience our environment and to make that experience more pleasant

1. SPECIAL SENSES

2. PHYSIOLOGY
PRESENTATION
Dr. Asra Hameed
Pharm.D (JUW)
[email protected]

3. SPECAL SENSES
Senses : any of the physical
processes by which stimuli are
received, transduced, and
conducted as impulses to be
interpreted in the brain.
The special senses consist of
the eyes, ears, nose, throat and
skin.
 Each of these organs have
specialized functions that
make if possible for us to
experience our environment
and to make that experience
more pleasant.

4. VISUAL SENSES
(EYE)
The human eye is astounding.
 Instead of being a camera, the eye
registers every new image, one
immediately after the other (about
20 per second).
In addition, because there are two
eyes, in-depth (binocular) vision is
accomplished.
 Because the eyeballs can move
separately, and the lens can
change thickness, we can see
things both closer and at a
distance.
The eye lies in a circular cavity
within several bones which, before
birth, fused together.
Each eye has optical equipment,
muscles, conjunctiva, tear
apparatus, and eyelids.

5. VISUAL SENSES
(EYE)
Here is a very simplified description of the many
wonders in the eye:
Eyeball: the white of the eye is the sclera.
Inside that is the colored part, or iris.
Inside that is the black spot, the pupil.
Light passes into the eyeball through the pupil, which can
enlarge (dilate) or shrink (contract) in size.
Behind the pupil, the light travels through the lens,
double convex in shape.
Behind that is a clear fluid throughout the middle of the
eyeball (vitreous humor).

6. VISUAL SENSES
(EYE)
At the back of the
eyeball, the light strikes
the retina, which contains
nerve fibers of the optic
nerve and the nerve cells
sensitive to light.
Light enters the front of
the eye through the pupil
and is focused by the lens
onto the retina. Rod cells
on the retina respond to
the light and send a
message through the
optic nerve fiber

7. VISUAL SENSES
(EYE)
Two types of cells are there: rods and cones.
There are 100 million rods in each retina, which can see
things as light and dark (black and white), even in very
dim light.
There are less cones; they see color, but only in brighter
light.
This is why, at night, you only see objects as dark and
light, without any color to them.
The lens bends thicker or thinner in order to focus the
light into a sharp image. This focusing is
called accommodation.
The light image is then carried to the cells and nerves in
the retina and is sent through the optic nerve, to the sight
center in the brain.

8. NERVOUS PATHWAYS FROM
THE RETINAS
 The two optic nerves enter the
cranial cavity and join in a
structure known as the optic
chiasma.
 Leading from the optic chiasma
on either side of the brainstem is
the optic tract.
 In the optic chiasma, the axons
from the nasal (medial) halves of
the retinas cross to the opposite
sides.
 Thus, the left optic tract
contains all of the information
from the left halves of the retinas
(right visual field), and the right
optic tract contains all of the
information from the right
halves of the retinas (left visual
field).

9. NERVOUS PATHWAYS FROM
THE RETINAS
The optic tracts carry this information to the LGB
(lateral geniculate body) of the thalamus.
From here, information is carried to the posterior medial
portions (occipital lobes) of the cerebral cortex, where the
information is perceived as conscious vision.
Note that the right visual field is perceived within the left
hemisphere, and the left visual field is perceived within
the right hemisphere.
The LGB also sends information into the midbrain stem.
This information is used to activate various visual
reflexes.

10. THE SPECIAL SENSE OF HEARING
(AUDITORY SENSE)
INTRODUCTION
If a medium is set into
vibration within certain
frequency limits (average
between 25 cycles per
second and 18,000 cycles
per second), we have
what is called a sound
stimulus. The sensation of
sound, of course, occurs
only when these
vibrations are interpreted
by the cerebral cortex of
the brain at the conscious
level.

11. AUDITORY SENSE
The human ear is the special sensory receptor for
the sound stimulus. As the stimulus passes from
the external medium (air, water, or a solid
conductor of sound) to the actual receptor cells in
the head, the vibrations are in the form of (1)
airborne waves, (2) mechanical oscillations, and
(3) fluid-borne pulses.
The ear is organized in three major parts:
external ear, middle ear, and internal (inner) ear.
Each part aids in the transmission of the stimulus
to the receptor cells.

13. THE EXTERNAL EAR
The external ear begins with a funnel-like auricle.
This auricle serves as a collector of the airborne
waves and directs them into the external auditory
meatus.
At the inner end of this passage, the waves act
upon the tympanic membrane (eardrum).
The external auditory meatus is protected by a
special substance called earwax (cerumen).

14. THE MIDDLE EAR
Tympanic
Membrane. The
tympanic membrane
separates the middle
and external ears. It
is set into mechanical
oscillation by the
airborne waves from
the outside.
Middle Ear Cavity.
Within the petrous
bone of the skull is
the air-filled middle
ear cavity.

15. THE MIDDLE EAR
 Function of the auditory tube. Due to the auditory tube, the air of
the middle ear cavity is continuous with the air of the surrounding
environment. The auditory tube opens into the lateral wall of the
nasopharynx. Thus, the auditory tube serves to equalize the air
pressures on the two sides of the tympanic membrane. If these two
pressures become moderately unequal, there is greater tension upon
the tympanic membrane; this reduces (dampens) mechanical
oscillations of the membrane. Extreme pressure differences cause
severe pain. The passage of the auditory tube into the nasopharynx
opens when one swallows; therefore, the pressure differences are
controlled somewhat by the swallowing reflex.
Associated spaces. The middle ear cavity extends into the mastoid
bone as the mastoid air cells. The relatively thin roof of the middle
ear cavity separates the middle ear cavity from the middle cranial
fossa.

16. THE MIDDLE EAR
 Auditory Ossicles. There is a series of three small bones, the auditory
ossicles, which traverse the space of the middle ear cavity from the
external ear to the internal ear. The auditory ossicles function as a unit.
(1) The first ossicle, the malleus, has a long arm embedded in the
tympanic membrane. Therefore, when the tympanic membrane is set
into mechanical oscillation, the malleus is also set into mechanical
oscillation.
(2) The second ossicle is the incus. Its relationship to the malleus
produces a leverage system which amplifies the mechanical
oscillations received through the malleus.
(3) The third ossicle, the stapes, articulates with the end of the arm of
the incus. The foot plate of the stapes fills the oval (vestibular)
window.
 Auditory Muscles. The auditory muscles are a pair of muscles associated
with the auditory ossicles. They are named the tensor tympani muscle
and the stapedius muscle. The auditory muscles help to control the
intensity of the mechanical oscillations within the ossicles.

17. THE INTERNAL EAR
Transmission of the Sound Stimulus. The foot plate of
the stapes fills the oval (vestibular) window, which opens
to the vestibule of the internal ear . As the ossicles
oscillate mechanically, the stapes acts like a plunger
against the oval window. The vestibule is filled with a
fluid, the perilymph. These mechanical, plunger-like
actions of the stapes impart pressure pulses to the
perilymph.
 Organization of the Internal Ear. The internal ear is
essentially a membranous labyrinth suspended within
the cavity of the bony (osseous) labyrinth of the petrous
bone. The membranous labyrinth is filled with a fluid,
the endolymph. Between the membranous labyrinth and
the bony labyrinth is the perilymph.

18. THE INTERNAL EAR

19. THE INTERNAL EAR
 The Cochlea. The cochlea is a spiral structure associated with hearing.
Its outer boundaries are formed by the snail-shaped portion of the bony
labyrinth. The extensions of the bony labyrinth into the cochlea are
called the scala vestibuli and the scala tympani. These extensions are
filled with perilymph.
Basilar membrane The basilar membrane forms the floor of the cochlear
duct, the spiral portion of the membranous labyrinth. The basilar membrane
is made up of transverse fibers. Each fiber is of a different length, and the
lengths increase from one end to the other. Thus, the basilar membrane is
constructed similarly to a harp or piano. Acting like the strings of the
instrument, the individual fibers mechanically vibrate in response to specific
frequencies of pulses in the perilymph. Thus, each vibration frequency of
the sound stimulus affects a specific location of the basilar membrane.
Organ of Corti. Located upon the basilar membrane is the organ of Corti.
The organ of Corti is made up of hair cells. When the basilar membrane
vibrates, the hair cells are mechanically deformed so that the associated
neuron is stimulated.

20. NERVOUS PATHWAYS FOR
HEARING
The neuron (associated with the hair cells of the organ of
Corti) then carries the sound stimulus to the
hindbrainstem.
Via a special series of connections, the signal ultimately
reaches Brodmann's area number 41, on the upper
surface of the temporal lobe .
Here, the stimulus is perceived as the special sense of
sound. It is interesting to note that speech in humans is
primarily localized in the left cerebral hemisphere, while
musical (rhythmic) sounds tend to be located in the right
cerebral hemisphere.

21. TASTE
Taste is mainly a function of taste buds
In mouth taste buds are present
PRIMARY SENSATION:
 In taste cell 13 chemical receptor are present
 2 sodium,2 potassium,1 chloride,1 adenosine,,1
inosine,2 sweet,2 bitter,1 glutamate and 1
hydrogen ion receptor
For practically analysis of taste they are grouped
in 5 general categories called primary sensation
of taste they are sour,salty,bitter,sweet and
umami.

22. TASTE
SOUR
Sour taste is caused by H ion conc.
More H ion conc. more acidic food stronger the sour sensation
SALTY:
 salty taste is caused by sodium ion conc.
Cat ion of sodium is responsible for salty taste
SWEET TASTE:
 chemical like sugar, glycol, alcohol, aldehyde, amides, ester and organic
compound cause sweet taste
BITTER:
 two particular class cause bitter taste
Long chain organic substance that contain nitrogen
 Alkaloids (including caffeine and nicotine)
UMAMI:
Umami taste of food containing L-glutamate pleasant taste sensation

23. TASTE
TASTE BUDS AND ITS FUNCTIONS
Diameter of taste buds is 1/30 millimeter.
Length of about 1/16 millimeter.
 composed of 50 modified epithelial cell.
 life span is 10 days.
In taste cell outer tip pores, microvili n taste
hairs are present
LOCATION OF TASTE BUDS:
3 types of papillae of the tongue
Large number on the wall of the troughs
(posterior tongue)
Moderate number are on fungi form papillae
(anterior tongue)
Moderate number on the foliate papillae
(lateral tongue)
Transmission of taste signals into the CNS.
Through neural pathway

24. (GUSTATION)
SENSORY RECEPTORS
Molecules of various materials are also dispersed
or dissolved in the fluids (saliva) of the mouth.
These molecules are from the food ingested
(taken in).
Organs known as taste buds are scattered over
the tongue and the rear of the mouth.
 Special hair cells in the taste buds are
chemoreceptors to react to these molecules.
SENSORY PATHWAY
The information received by the hair cells of the
taste buds is transmitted to the opposite side of
the brain by way of three cranial nerves (VII, IX,
and X).
This information is interpreted by the cerebral
hemispheres as the sensation of taste.

25. SENSE OF SMELL
• The physiology of smell in
humans begins in the nasal cavity.
• There, a huge number of
receptors (over 40 million) are
located in the upper roof of the
cavity
• The receptors have cilia
projections that stick out into the
cavity space.
• These increase the surface area
and the sensitivity of the receptors.

26. SENSE OF SMELL
One reason for the receptor sensitivity concerns
the mechanics of airflow in the nasal cavity.
The air rushes in quickly (at about 250
milliliters per second) and is turbulent.
Thus, not all of a particular odor will have a
chance to contact a receptor.
So, a receptor must be able to swiftly detect a
low concentration of a molecule.

27. SENSE OF SMELL
•The olfactory receptor cells
are replaced every three to
four weeks.
•The receptors are responsible
for detecting a large number of
odours (about 2,000, depending
on the individual).
•A group of genes is known to
encode proteins associated with
the receptors that may function
in the specific detection of an
odor.
•There may be upwards of 1,000
very specific odor receptors.

28. SENSE OF SMELL
•Odors reach a receptor by diffusing through the air and physically contacting the
receptor.
•Surrounding the cilia is a mucous membrane.
• It is into this membrane that an odor dissolves.
•The binding of an odor molecule to a receptor stimulates the activation of a protein
called the G-protein and the release of calcium from the receptor membrane.
•These events begin the process whereby an electrical potential is generated.
•The potential constitutes the signal that is sent off to the brain.
•A signal is relayed to the anterior olfactory nucleus, which is essentially a collection
point for the receptor signals.
•The signals are then routed to a region of the brain responsible for the processing of
the information.
•This region is known as the primary olfactory cortex.
•Following the stimulation of a receptor, the odor molecule is rapidly destroyed and
the stimulation ended.
•This frees the receptor for stimulation by another odor molecule.
•In this way the sensitivity of the smell sensory system is maintained.

29. ABNORMALITIES
•Anosmia – absence of sense of smell
•Hyposmia – diminished olfactory sensitivity
•Dysosmia – distorted sense of smell
•More than 75% of humans over the age of 80
have an impaired ability to identify smells

30. SOMATIC
SENSATIONS(TOUCH)
The somatic sensation
are the nervous
mechanisms that
collect sensory
information for all over
the body.
Somatosensory
system consist of ;
Receptors
Transmitters
S1

32. CLASSIFICATION OF SOMATIC
SNESATION:
The somatic sensation can be
classified into three
physiological types:
 The mechanoreceptive
somatic senses (tactile and
position)
 The thermoreceptive senses
(heat and cold).
 The pain senses.
Other classification includes:
 Exteroreceptive sensation
 Proprioception sensation
 Visceral sensation
 Deep sensation

33. PHYSIOLOGY OF
SOMATOSENSATION
Initiation of somato sensation begins
with activation of a physical
“RECEPTOR”
Receptors having similar structure in
all cases can be activated by
Mechanoreceptor or Chemoreceptor.
Another activation by vibration
generated as a finger scans across a
surface.
The general principle of activation is
similar.
The stimulus causes depolarization of
the nerve ending & then an action
potential is initiated.
This action potential then (usually)
travels inwards-towards the Spinal
Cord.